Abstract:

A catalyst supporting honeycomb including a pillar-shaped honeycomb
structure having a plurality of cells formed in parallel with one another
in a longitudinal direction with a cell wall interposed therebetween, and
catalyst particles supported on the honeycomb structure. The catalyst
particles include an oxide catalyst, an average particle diameter of
which is at least about 0.05 μm and at most about 1.00 μm.

Claims:

1. A catalyst supporting honeycomb comprising:a pillar-shaped honeycomb
structure having a plurality of cells formed in parallel with one another
in a longitudinal direction with a cell wall interposed therebetween;
andcatalyst particles supported on the honeycomb structure,said honeycomb
structure primarily comprising inorganic fibers,said catalyst particles
being configured by an oxide catalyst having an average particle diameter
of at least about 0.05 μm and at most about 1.00 μm.

2. The catalyst supporting honeycomb according to claim 1,whereineither of
two end portions of each of said cells is sealed.

3. The catalyst supporting honeycomb according to claim 1,whereinsaid
honeycomb structure is formed by a plurality of lamination members
laminated with one another in a longitudinal direction, andsaid
lamination members are laminated so that the cells of each lamination
member are aligned with the cells of the other lamination members.

4. The catalyst supporting honeycomb according to claim 1,whereina
porosity of said cell wall is about 70% or more.

5. The catalyst supporting honeycomb according to claim 1,whereinsaid
oxide catalyst is at least one member selected from the group consisting
of CeO2, ZrO2, FeO2, Fe2O3, CuO, CuO2,
Mn2O3, MnO, K2O, and a composite oxide represented by a
composition formula AnB1-nCO3 in which A represents La,
Nd, Sm, Eu, Gd or Y; B represents an alkali metal or an alkali earth
metal; and C represents Mn, Co, Fe or Ni.

6. A catalyst supporting honeycomb comprising:a pillar-shaped honeycomb
structure having a plurality of cells formed in parallel with one another
in a longitudinal direction with a cell wall interposed therebetween,
said cell wall primarily comprising inorganic fibers, andoxide catalyst
particles supported on the cell wall, said oxide catalyst particles being
supported by flowing a gas containing a dispersed solution of a precursor
of the oxide catalyst into the honeycomb structure.

7. A method of manufacturing a catalyst supporting honeycomb, the method
comprising:manufacturing a honeycomb structure having a plurality of
cells formed in parallel with one another in a longitudinal direction
with a cell wall interposed therebetween, said cell wall primarily
comprising inorganic fibers;dispersing a solution of a precursor of a
catalyst in a gas;flowing a gas containing the dispersed solution of the
precursor of the catalyst into said honeycomb structure; andheating said
honeycomb structure so that the precursor of the catalyst is formed into
catalyst particles.

Description:

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001]This present application claims priority under 35 U.S.C. §119
to PCT Application No. PCT/JP2007/058375, filed Apr. 17, 2007, the
contents of which are incorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

[0002]1. Field of the Invention

[0003]The present invention relates to a catalyst supporting honeycomb and
a method of manufacturing the same.

[0004]2. Discussion of the Background

[0005]There has been known a catalyst supporting honeycomb which converts
exhaust gases by allowing the exhaust gases to contact with a catalyst
supported on cell walls of a honeycomb structure which is mainly made of
inorganic fibers. With regard to a catalyst supporting honeycomb
disclosed in WO 2007/10643 A1, a catalyst is supported on a honeycomb
structure by impregnating the honeycomb structure in a catalyst solution
in a slurry state, and then heating the honeycomb structure.

[0006]The contents of WO 2007/10643 A1 are incorporated herein by
reference in their entirety

SUMMARY OF THE INVENTION

[0007]A catalyst supporting honeycomb of the present invention includes a
pillar-shaped honeycomb structure having a plurality of cells formed in
parallel with one another in a longitudinal direction with a cell wall
interposed therebetween; and catalyst particles supported on the
honeycomb structure. The honeycomb structure primarily includes inorganic
fibers. The catalyst particles are configured by an oxide catalyst having
an average particle diameter of at least about 0.05 μm and at most
about 1.00 μm.

[0008]A method for manufacturing a catalyst supporting honeycomb of the
present invention includes manufacturing a honeycomb structure having a
plurality of cells formed in parallel with one another in a longitudinal
direction with a cell wall interposed therebetween. The cell wall
primarily includes inorganic fibers. The method further includes
dispersing a solution of a precursor of a catalyst in a gas; flowing a
gas containing the dispersed solution of the precursor of the catalyst
into the honeycomb structure; and heating the honeycomb structure so that
the precursor of the catalyst is formed into catalyst particles.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009]A more complete appreciation of the invention and many of the
attendant advantages thereof will be readily obtained as the same becomes
better understood by reference to the following detailed description when
considered in connection with the accompanying drawings, wherein,

[0010]FIG. 1A shows a state of catalysts supported by a conventional
method and soot, and FIG. 1B shows a state of the catalysts supported by
an embodiment of the present invention and soot;

[0011]FIG. 2 is a cross sectional diagram that schematically illustrates a
portion of the inorganic fiber forming the honeycomb structure according
to the embodiment of the present invention;

[0012]FIG. 3 is a cross-sectional diagram that schematically illustrates a
plunger-type molding machine to be used for molding a pillar-shaped
molded body;

[0013]FIG. 4A is a perspective view that shows the honeycomb structure and
the lamination members forming the honeycomb filter according to
embodiment of the present invention, and FIG. 4B is a perspective view
that shows a state in which the honeycomb structure and the lamination
members shown in FIG. 4A are laminated to manufacture the honeycomb
filter;

[0014]FIG. 5 is a graph that shows a relationship between influx amount of
soot and pressure loss;

[0015]FIG. 6 is a table graph that shows the prescribed temperatures of
filters and the flow rate of gases flowing into the filters; and

[0016]FIG. 7 is a graph that shows oxidation rate of soot by Arrhenius
plot.

DESCRIPTION OF THE EMBODIMENT

[0017]The embodiments will now be described with reference to the
accompanying drawings, wherein like reference numerals designate
corresponding or identical elements throughout the various drawings.

[0018]According to an embodiment of the present invention, oxide catalyst
particles are supported on a pillar-shaped honeycomb structure primarily
comprising inorganic fibers, in which a plurality of cells are formed in
parallel with one another in a longitudinal direction with a cell wall
interposed therebetween, and the average particle diameter of the oxide
catalyst particles is set to at least about 0.05 μm and at most about
1.00 μm.

[0019]In the embodiment of the present invention, since either of two end
portions of each cell is sealed, cell walls of the catalyst supporting
honeycomb function as filter for capturing soot.

[0020]In the embodiment of the present invention, the average particle
diameter of the oxide catalyst particles supported thereon is set to at
least about 0.05 μm and at most about 1.00 μm, which is almost the
same as an average particle diameter of the secondary particles of soot.
Therefore, the activity points between the secondary particles of soot
and the catalyst particles can be increased as shown in FIG. 1B. In other
words, the soot and the catalyst can easily contact with each other, with
the result that the soot combustion behavior by active oxygen induced by
the oxide catalyst can be more easily improved.

[0021]This behavior, in addition to the forced regeneration of soot flowed
into the catalyst supporting honeycomb, makes it easier to combust soot
as compared with the catalyst supporting honeycomb of WO 2007/10643 A1.
As a result, it becomes easier to reduce an increase with time in the
pressure loss upon an influx of soot.

[0022]Normally, the average diameter of secondary particles of soot in
exhaust gases is about 0.1 μm. However, in the catalyst supporting
honeycomb disclosed in WO 2007/10643 A1, since the honeycomb structure
has been impregnated in the catalyst solution in a slurry state, the
diameter of the supported catalyst particles 202 tends to be much larger
than the diameter of the secondary particles 201 of soot as shown in FIG.
1A. Accordingly, this prior art tends to have a problem that, due to few
activity points 203 between the catalyst particles and the secondary
particles of soot, soot combustion behavior by active oxygen induced by
an oxide catalyst cannot be fully exerted.

[0023]Accordingly, soot captured by the catalyst supporting honeycomb of
this kind becomes less likely to be combusted, except for by forced
regeneration using high temperature exhaust gases. Therefore, soot is
easily accumulated on cell walls, causing a problem of increase with time
in the pressure loss due to an influx of soot into the catalyst
supporting honeycomb.

[0024]According to the embodiment of the present invention, it becomes
easier to suppress an increase with time in the pressure loss upon an
influx of soot into catalyst supporting honeycombs in which a catalyst is
supported, by allowing soot that has been flowed in to more easily
contact with the catalyst with each other so as to improve the soot
combustion behavior by active oxygen induced by the oxide catalyst.

[0025]Meanwhile, in the embodiment of the present invention, even in the
case where the end portion is not sealed, the exhaust gas converting
performance can be more easily improved due to the increased chance of
contact between exhaust gases and the catalyst.

[0026]In the embodiment of the present invention, the catalyst supporting
honeycomb can also be concretely configured by a honeycomb structure in
which a plurality of lamination members are laminated with one another in
a longitudinal direction, and the lamination members are laminated so
that the cells of each lamination member are aligned with the cells of
the other lamination members.

[0027]Moreover, in the embodiment of the present invention, the porosity
of the cell wall is about 70% or more. With this structure, soot can be
more easily flowed into deep portions of the cell walls. Accordingly, the
catalyst supported inside the cell walls can be more easily contacted
with the soot, resulting in improved combustion of the soot that has
flowed into the catalyst supporting honeycomb. This effect makes it
possible to extend a time period during which soot is flowed into deep
portions of the cell walls, and consequently a time period before a surge
of pressure loss can be prolonged.

[0028]Further, in the embodiment of the present invention, when the oxide
catalyst is at least one member selected from the group consisting of
CeO2, ZrO2, FeO2, Fe2O3, CuO, CuO2,
Mn2O3, MnO, K2O, and a composite oxide represented by a
composition formula AnB1-nCO3 (in which A represents La,
Nd, Sm, Eu, Gd or Y; B represents an alkali metal or an alkali earth
metal; C represents Mn, Co, Fe or Ni), a catalyst which is excellent in
active oxygen delivery performance can be supported on the catalyst
supporting honeycomb. As a result of this, in particular, the soot
combustion function of the catalyst supporting honeycomb can be more
easily improved.

[0029]Furthermore, in the embodiment of the present invention, when a gas
containing a dispersed solution of a precursor of an oxide catalyst is
flowed into a pillar-shaped honeycomb structure configured by a plurality
of cells formed in parallel with one another in a longitudinal direction
with a cell wall, which primarily includes inorganic fibers, interposed
therebetween, the catalyst supporting honeycomb, in which the oxide
catalyst particles are supported on the cell walls, can show the same
effects as those specifically described above.

[0030]Moreover, by employing a method of manufacturing a catalyst
supporting honeycomb according to the embodiment of the present
invention, which includes processes of: manufacturing a honeycomb
structure configured by a plurality of cells formed in parallel with one
another in a longitudinal direction with a cell wall, which primarily
includes inorganic fibers, interposed therebetween; dispersing a solution
of a precursor of a catalyst in a gas; flowing a gas containing the
dispersed solution of the precursor of the catalyst into the honeycomb
structure; and heating the honeycomb structure so that the precursor of
the catalyst is formed into catalyst particles, it is possible to
manufacture a catalyst supporting honeycomb which can show the same
effects as those specifically described above.

[0031]In the following, a plurality of embodiments of the present
invention are described with reference to drawings.

First Embodiment

[0032]The following description will discuss a honeycomb structure
primarily comprising inorganic fibers according to a first embodiment of
the present invention with reference to drawings.

[0033]The honeycomb structure according to the present embodiment is
configured by inorganic fibers and inorganic material, and the inorganic
fibers are fixed to each other through the inorganic material. Here,
portions where the inorganic fibers are fixed to each other are mainly
intersection portions of the inorganic fibers, and the inorganic material
is preferably present locally at the intersection portions of the organic
fibers. Preferably, the inorganic material fixes the intersection
portions of the inorganic fibers by vitrification. Here, the honeycomb
structure according to the present embodiment is an integral honeycomb
structure comprising a single member.

[0034]FIG. 2 is a cross sectional diagram that schematically illustrates a
portion of the inorganic fiber forming the honeycomb structure according
to the present embodiment. Here, the cross sectional diagram shown in
FIG. 2 is a cross sectional diagram obtained by cutting the crossing
inorganic fibers in a length direction.

[0035]When inorganic material 62 is fixed to an intersection portion of
inorganic fibers 61 which form the honeycomb structure as shown in FIG.
2, the inorganic material 62 fixed to the intersection portion functions
to bond the two inorganic fibers at the intersection portion. The fixing
portion is present not only at one site but also at two or more sites per
one inorganic fiber, causing complex intertwining of many fibers, and
therefore, separation of the inorganic fibers can be avoided. Moreover,
strength of the honeycomb structure is improved.

[0036]In the case where the inorganic material 62 is locally present at
the intersection portions of inorganic fibers 61, in many of the
inorganic fibers 61, intersection portions with other organic fibers 61
are coated with the organic material 62, and almost no inorganic material
is fixed to most of the rest portions of the inorganic fibers 61.

[0037]Here, the intersection portion of the inorganic fibers refers to an
area within a distance of about ten times of the fiber diameter of the
inorganic fibers from the portion where inorganic fibers are most close
to each other.

[0038]The above-mentioned honeycomb structure is configured by inorganic
fibers and inorganic material. Examples of the inorganic fibers include:
an oxide ceramic such as silica-alumina, mullite, alumina, silica,
titania and zirconia; a nitride ceramic such as silicon nitride and boron
nitride; a carbide ceramic such as silicon carbide; basalt, and the like.
Each of these materials may be used alone, or two or more of them may be
used in combination

[0039]An example of the inorganic material includes inorganic material
that melts at a temperature at which the inorganic fibers neither melt
nor sublime. Moreover, the inorganic material preferably includes
inorganic material that melts at a temperature of the heat-resistant
temperature of the inorganic fibers or lower.

[0040]Here, in consideration of the temperature at which the inorganic
fibers to be combined melt or sublime, the heat resistance temperature of
the inorganic fibers or the like, for example, those inorganic materials
which melt at a temperature of the heat-resistant temperature of the
inorganic fibers or less may be used. More specifically, for example, in
the case where alumina is used as the inorganic fibers, those inorganic
materials which melt at about 1300° C. or less may be used.

[0041]With respect to the inorganic material, those containing silica are
preferably used, and specific examples of the inorganic material
containing silica include inorganic glass such as silicate glass,
silicate alkali glass and borosilicate glass, and the like.

[0042]With respect to the porosity of the cell walls of the honeycomb
structure according to the embodiment of the present invention, the
desirable lower limit is about 70%, and the desirable upper limit is
about 95%. When the porosity is about 70% or more, soot tends to enter
into inner portions of pores, and as a result, those catalysts supported
on the inner portions of the cell walls of the honeycomb structure tend
to contact with soot. On the other hand, when the porosity is about 95%
or less, the ratio occupied by pores tends not increase, and therefore it
becomes easier to maintain the strength of the honeycomb structure as a
whole.

[0043]In the honeycomb structure according to the embodiment of the
present invention, an average pore diameter is not specifically limited,
and the desirable lower limit is about 10 μm, and the desirable upper
limit is about 100 μm. When the average pore diameter is about 10
μm or more, the catalyst is more easily supported on the inner
portions of the cell walls, and also soot may be more easily filtered at
the deep inside the cell walls, with the result that the soot is more
easily made in contact with the catalyst supported on the inner portions
of the cell walls. On the other hand, when the average pore diameter is
about 100 μm or less, a catalyst or soot may not easily pass through
the pores, and thus more easily function as a filter.

[0044]Here, the above-mentioned porosity and pore diameter can be measured
through known methods, such as a measuring method using a mercury
porosimeter, Archimedes method and a measuring method using a scanning
electron microscope (SEM).

[0045]With regard to the aperture ratio of the honeycomb structure
according to the embodiment of the present invention, the desirable lower
limit is about 30%, and the desirable upper limit is about 60%. When the
aperture ratio is about 30% or more, the pressure loss tends not become
high when exhaust gases flow into and out of the honeycomb structure.
When the aperture ratio is about 60% or less, the strength of the
honeycomb structure becomes less likely to be reduced.

[0046]A method of manufacturing the honeycomb structure according to the
present embodiment includes process of: mixing inorganic fibers A with
inorganic fibers B and/or inorganic particles C, both of which melt at a
temperature at which the inorganic fibers A neither melt nor sublime;
extrusion-molding a mixture obtained by the above-mentioned mixing
process through a die in which predetermined holes are formed to form a
pillar-shaped molded body with a number of cells formed in the
longitudinal direction; and carrying out a heating treatment on the
molded body at a temperature of the heat-resistant temperature of the
inorganic fibers A or less and at the same time at a temperature of the
softening temperature of the inorganic fibers B and/or the inorganic
particles C or more.

[0047]The following description will discuss the above-mentioned
manufacturing method of the honeycomb structure in order of the
processes. First, a mixing process is carried out by mixing the inorganic
fibers A with the inorganic fibers B and/or the inorganic particles C,
both of which melt at a temperature at which the inorganic fibers A
neither melt nor sublime, so as to prepare a mixture.

[0048]The same inorganic fibers exemplified in the description of the
honeycomb structure mentioned above can be used as the inorganic fibers
A. The preferable examples thereof include at least one member selected
from the group consisting of silicon carbide, alumina, basalt, silica,
silica-alumina, titania and zirconia, because this arrangement makes it
possible to manufacture a honeycomb structure having excellent heat
resistance.

[0049]The inorganic fibers B and/or the inorganic particles C are not
particularly limited as long as the inorganic fibers and/or the inorganic
particles melt at a temperature at which the inorganic fibers A do not
melt. Specifically, examples of the inorganic fibers B include inorganic
glass fibers comprising silicate glass, silicate alkali glass,
borosilicate glass and the like, or the like, and examples of the
inorganic particles C include inorganic glass particles comprising
silicate glass, silicate alkali glass, borosilicate glass and the like,
or the like.

[0050]When the inorganic fibers A is mixed with the inorganic fibers B
and/or the inorganic particles C, the blending ratio (weight ratio)
between the inorganic fibers A and a total amount of the inorganic fibers
B and the inorganic particles C preferably is at least about (2:8) and at
most about (8:2). When the blending ratio of the inorganic fibers A is
about (2:8) or more, the inorganic material is less likely to fix to the
inorganic fibers in a manner as to coat the surface of the inorganic
fibers, and thus flexibility in the resulting honeycomb structure is more
likely to be sufficient. In contrast, when the blending ratio of the
inorganic fibers A is about (8:2) or less, the fixing portions between
the inorganic fibers are less likely to decrease, and thus strength in
the resulting honeycomb structure is more likely to be sufficient.

[0051]Here, in preparation of the above-mentioned mixture, a liquid medium
such as water, or a dispersant may be added thereto, if necessary, so as
to uniformly mix the inorganic fibers A with the inorganic fibers B
and/or the inorganic particles C. Moreover, an organic binder may be
added thereto. When the inorganic binder is added, the inorganic fibers A
can be surely entangled with the inorganic fibers B and/or the inorganic
particles C so that, even prior to a firing process, the inorganic fibers
B and/or the inorganic particles C are made to be hardly drawn off from
the inorganic fibers A; thus, it becomes easier to more surely fix the
inorganic fibers A to one another.

[0052]Examples of the organic binder include: an acrylic binder, ethyl
cellulose, butyl cellosolve, polyvinyl alcohol and the like. One kind of
these organic binders may be used, or two or more kinds of these may be
used in combination. In addition, if necessary, a plasticizer, a
lubricant, a molding auxiliary, a pore-forming agent and the like may be
added thereto. With respect to the plasticizer and the lubricant, those
conventionally used may be applied.

[0053]The thus obtained mixture is preferably allowed to have such
properties that the homogeneous composition is maintained for a long time
and that the inorganic fibers and the like are prevented from
precipitating, and further, the mixture is preferably allowed to have a
degree of viscosity that can maintain the predetermined shape in the
succeeding molding process.

[0054]Next, an extrusion-molding process is carried out on the mixture
obtained in the above-mentioned mixing process. In this extrusion-molding
process, the mixture is continuously extruded by using a die in which
predetermined holes are formed so as to form a pillar-shaped molded body
with a large number of cells formed in the longitudinal direction.

[0055]The apparatus to be used in the extrusion-molding process is not
particularly limited, and for example, a single-axis screw-type
extrusion-molding machine, a multi-axis screw-type extrusion-molding
machine, a plunger-type molding machine and the like may be used. Among
these, in particular, the plunger-type molding machine is preferably
used.

[0056]With reference to the drawings, the following description will
discuss a plunger-type molding machine to be used in the present process
and the application example thereof, although not limited to those
systems.

[0057]FIG. 3 is a cross-sectional diagram that schematically illustrates a
plunger-type molding machine to be used for molding a pillar-shaped
molded body.

[0058]This plunger-type molding machine 80 is formed by a cylinder 81, a
piston 83 provided with a mechanism capable of reciprocally moving
between the front side and the rear side in the cylinder (horizontal
direction in the figure), a die 84 that is attached to the tip of the
cylinder and has holes formed therein for extrusion-molding a
pillar-shaped molded body with a large number of cells formed in the
longitudinal direction, and a mixture tank 82 placed on the upper portion
of the cylinder 81, to which a pipe 85 is connected from the cylinder 81.
Moreover, a shutter 86 is placed right below the mixture tank 82 so that
the charging operation of the mixture from the mixture tank 82 can be
interrupted. Here, a screw 87 with blades 87a is attached to the pipe 85,
and allowed to rotate by a motor 88. The size of the blade 87a is set to
virtually the same as the diameter of the pipe so that the mixture 89 is
hardly allowed to flow reversibly. The mixture prepared in the
above-mentioned mixing process is loaded into the mixture tank 82.

[0059]In manufacturing a molded body by using the plunger-type molding
machine 80, first, the shutter 86 is opened, and the mixture, obtained in
the mixing process, is charged into the cylinder 81 from the mixture tank
82 by rotating the screw. At this time, the piston 83 is moved to the end
portion of the cylinder 81 on the right side in FIG. 3 according to the
amount of the charge.

[0060]When the cylinder 81 is filled in with the mixture, the shutter 86
is closed and the rotation of the screw 87 is simultaneously stopped.
When the piston 83 is pressed and shoved into the die side with the
inside of the cylinder 81 filled with the mixture 89, the mixture is
extruded through the die 84 so that a pillar-shaped molded body in which
a plurality of cells are formed with a wall portion therebetween is
continuously formed. At this time, according to the shape of the hole
formed in the die, cells having the corresponding shape are formed. By
repeating these processes, a molded body can be manufactured. Depending
on the viscosity and the like, a molded body can be continuously
manufactured, by rotating the screw 87 while the cylinder 83 is stopped.

[0061]Here, in the plunger-type molding machine 80 illustrated in FIG. 3,
an oil cylinder 80 is used as the driving source used for shifting the
piston 83; however, an air cylinder may be used, or a ball screw or the
like may also be used.

[0062]The shape of the cells to be formed through the extrusion-molding
process can be desirably selected by changing the shape of holes to be
formed in the die.

[0063]The shape on the vertical cross section of each of the cells is not
particularly limited to a tetragonal shape, and any desired shape such as
a triangular shape, a hexagonal shape, an octagonal shape, a dodecagonal
shape, a round shape, an elliptical shape and a star shape may be listed.

[0064]Moreover, molded bodies having various outer shapes can be
manufactured by changing the shape of the die. The vertical
cross-sectional shape of the honeycomb structure is not limited to a
round shape, and various shapes such as a rectangular shape may be used;
however, it is preferable to use a shape enclosed only by a curved line
or by curved lines and straight lines. Specific examples thereof include,
in addition to a round shape, a rectangular pillar shape, an elongated
round shape (racetrack shape), a shape in which one portion of a simple
closed curved line such as a rectangular pillar shape or a racetrack
shape has a recess portion (concave shape), and the like.

[0065]Next, heating treatment is carried out on the molded body obtained
in the above-mentioned extrusion-molding process. In this heating
treatment process, the molded body is heated at a temperature of the
heat-resistant temperature of the inorganic fibers A or less and at the
same time at the softening temperature of the inorganic fibers B and/or
the inorganic particles C or more; thus, a honeycomb structure is
obtained.

[0066]By carrying out this heating treatment, it is possible to
manufacture a honeycomb structure in which the inorganic fibers A are
firmly fixed to one another through an inorganic material comprising the
same material as the inorganic fibers B and/or the inorganic particles C,
and most of the firmly fixed portions are the intersections of the
inorganic fibers A, and the inorganic materials comprising the same
material as the inorganic fibers B and/or the inorganic particles C are
locally present at the intersections.

[0067]Here, the heating temperature is appropriately determined by taking
into consideration the combination of the inorganic fibers A with the
inorganic fibers B and/or the inorganic particles C.

[0068]Examples of the heat-resistant temperature of the inorganic fibers A
are given as follows: alumina>about 1300° C., silica>about
1000° C., silicon carbide>about 1600° C., and
silica-alumina>about 1200° C.

[0069]The specific heating temperature cannot be unconditionally
determined because it depends on the heat-resistant temperature and the
softening temperature of the inorganic fibers and the inorganic
particles, and it is preferably set to at least about 900° C. and
at most about 1050° C. in the case where inorganic glass is used
as the inorganic fibers B and/or the inorganic particles C.

[0070]Additionally, prior to the heating treatment process, it is
preferable to carry out a cutting process for cutting the manufactured
molded body into a predetermined length, a drying process for removing
moisture from the molded body and a degreasing process for removing
organic materials from the molded body.

[0071]The cutting member to be used in the cutting process is not
particularly limited, and for example, a cutter having a blade formed in
the cutting portion, a laser beam, a linear member, or the like may be
used. Moreover, a cutter that uses a rotary disc for cutting may also be
used.

[0072]Moreover, another preferable cutting method is proposed in which to
the end to which the molded body molded in the extrusion-molding process
is transferred, a molded body cutting machine provided with a cutting
means such as a laser and a cutter is installed, and while the cutting
means is being transferred at a speed synchronous to the extruding speed
of the molding body, the molded body is cut by the cutting means.

[0073]By using the cutting apparatus having the above-mentioned mechanism,
it is possible to carry out the cutting process continuously, and
consequently to improve the mass productivity.

[0074]With respect to the drying apparatus used for the drying process,
although not particularly limited, for example, a microwave heat drying
apparatus, a hot-air drying apparatus, an infrared ray drying apparatus
or the like may be used, and a plurality of these apparatuses may be used
in combination.

[0075]For example, in the case of using a hot-air drying apparatus, the
drying process is preferably carried out at a set temperature of at least
about 100° C. and at most about 150° C. for at least about
5 minutes and at most about 60 minutes under the atmospheric condition.
In this case, the arrangement is preferably made so that the hot air is
directed to the molded body in parallel with the longitudinal direction
thereof so as to allow the hot air to pass through the cells. By allowing
the hot air to pass through the cells of the molded body, the drying
process of the molded body is carried out efficiently.

[0076]Normally, the degreasing process is preferably carried out in an
oxidizing atmosphere such as normal atmosphere so as to oxidatively
decompose the organic substances. The degreasing furnace is not
particularly limited, and a batch-type degreasing furnace may be used;
however, in order to continuously carry out the process, a continuous
furnace provided with a belt conveyor is preferably used. The degreasing
process is preferably carried out by conducting a drying process at a set
temperature of at least about 200° C. and at most about
600° C. under normal atmosphere for at least about 1 hour and at
most about 5 hours.

[0077]In the method for manufacturing the honeycomb structure according to
the present embodiment, an acid treatment may be carried out on the
pillar-shaped molded body manufactured through the above-mentioned
method. By carrying out the acid treatment, the heat resistance of the
molded body can be improved. The acid treatment is carried out by
immersing the molded body in a solution such as a hydrochloric acid
solution and a sulfuric acid solution.

[0078]With respect to the conditions of the acid treatment, in the case
where inorganic glass is used as the inorganic material, the
concentration of the treatment solution is preferably at least about 1
mol/l and at most about 10 mol/l, the treating time is preferably at
least about 0.5 hours and at most about 24 hours, and the treatment
temperature is preferably at least about 70° C. and at most about
100° C. By carrying out the acid treatment under these conditions,
components other than silica are eluted so that the heat resistance of
the molded body is consequently improved.

[0079]The above-mentioned acid treatment process may be carried out during
heating treatment processes. More specifically, the following processes
are preferably carried out: a primary firing process is carried out at
about 950° C. for about 5 hours, and the acid treatment is then
carried out, and a heating treatment is again carried out at about
1050° C. for about 5 hours as a secondary firing process. These
processes are more likely to further improve the heat resisting property
of the molded body.

[0080]In the present embodiment, by laminating a honeycomb structure and a
lamination member for an end portion, it becomes easier to manufacture a
honeycomb filter functioning as a filter, in which either of two end
portions of each cell is sealed.

[0081]More specifically, as illustrated in FIG. 4B, by using a cylindrical
casing 11 (can-type metal container) with a pressing metal member on one
side, the lamination member for an end portion 10b is firstly laminated
in the casing 11, and the honeycomb structure 10a manufactured, for
example, according to the embodiment of the present invention is
installed thereon. Lastly, the lamination member 10b for an end portion
is laminated, and thereafter a pressing metal member is attached and
fixed also on the other side the casing 11 so that the honeycomb
structure on which processes up to a canning process have been carried
out can be manufactured. With respect to the material for the casing, for
example, metal materials such as stainless steel (SUS), aluminum and iron
may be used. Although not particularly limited, the shape of the casing
is preferably a shape similar to the outer shape of the honeycomb
structure to be housed.

[0082]With respect to the lamination member for an end portion, it is
preferable to laminate a lamination member for an end portion comprising
metal with predetermined through holes formed therein. With this
arrangement, it is possible to manufacture a honeycomb filter in which
the lamination member for an end portion mainly comprising metal is
laminated on both sides of the honeycomb structure.

[0083]As the lamination member for an end portion, a lamination member for
an end portion comprising inorganic fibers may be laminated. The
lamination member for an end portion comprising inorganic fibers may be
manufactured by the same method as the above-mentioned method of
manufacturing the honeycomb structure, except that the shape of the holes
formed in a die in the extrusion-molding process in the method for
manufacturing the honeycomb structure is changed so that a molded body
having cells formed in a checkered pattern is manufactured, and the
resulting molded body is thinly cut in the cutting process.

[0084]The method for manufacturing the lamination member for an end
portion comprising metal is described below.

[0085]A laser machining process or a punching process is carried out on a
porous metal plate mainly comprising metal having a thickness of at least
about 0.1 mm and at most about 20 mm so that a lamination member for an
end portion with through holes formed in a checkered pattern can be
manufactured.

[0086]Thereafter, an oxide catalyst is supported on the honeycomb
structure so that a catalyst supporting honeycomb is manufactured.

[0087]First, a solution of a precursor of a catalyst is prepared.
Preferable examples of the precursor of the catalyst include those that
become any of CeO2, ZrO2, FeO2, Fe2O3, CuO,
CuO2, Mn2O3, MnO, K2O, and a composite oxide
represented by a composition formula AnB1-nCO3 (in which A
represents La, Nd, Sm, Eu, Gd or Y; B represents an alkali metal or an
alkali earth metal; C represents Mn, Co, Fe or Ni), after such precursors
are condensed, thermally decomposed, and crystallized in the later
process. One kind of these precursors may be used, or two or more kinds
thereof may be used in combination. More specifically, for example,
nitrate salt, carbonate salt, acetate salt and the like containing a
metal element of the oxide can be used, and the examples thereof include
a metal complex body represented by a general formula
M(OR1)p(R2COCHCOR3)q (in the formula, M
represents one member selected from the group consisting of Ce, Zr, Fe,
Cu, Mn and K; p and q each represents an integer number determined so
that the metal complex has a 2 to 8 coordinate structure, and either p or
q may be 0; when the number of each of R1, R2 and R3 is
two or more, then R1, R2, R3 may be respectively the same
as or different. R1 and R2 each represents an alkyl group
having 1 to 6 carbon atoms, and R3 represents an alkyl group having
1 to 6 carbon atoms and/or an alkoxy group having 1 to 16 carbon atoms),
and the like. Examples of solvent include water, an organic solvent such
as toluene and alcohol, and the like.

[0088]The above-mentioned solution is dispersed in a gas by a known
spraying method and the like. When the dispersion is carried out in such
a manner that the dispersed droplets have a constant size, then the
particle diameter of the oxide catalyst to be supported on the honeycomb
structure in a later process can be adjusted to a constant size.

[0089]Next, the gas including the dispersed solution of the precursor is
transported by a carrier gas to flow into one of the ends of the
honeycomb structure 10a. At this time, the influx speed of the carrier
gas is preferably almost the same as the speed of actual exhaust gases
from an engine and may be, for example, about 72,000 (1/h) in terms of
space velocity. The carrier gas is flowed into one of the ends of the
honeycomb structure and flowed out from the adjacent cell after passing
through a cell wall. On this occasion, the solution of the precursor
dispersed and mixed in the carrier gas is adhered to the cell walls of
the honeycomb structure 10a.

[0090]Further, by heating the honeycomb structure at a temperature of at
least about 300° C. and at most about 800° C., the
precursor of the catalyst attached to the cell walls is condensed,
thermally decomposed and crystallized, and is supported on the honeycomb
structure as an oxide catalyst.

[0091]The oxide catalyst is supported preferably in such a manner that the
carrier gas is flowed into the honeycomb structure 10a while the
honeycomb structure 10a is heated so that adhesion of the solution of the
precursor as well as condensation, thermal decomposition and
crystallization of the precursor are performed simultaneously. With this
arrangement, the precursor of the catalyst is adhered to the honeycomb
structure as catalyst particles, and thus tends to be more evenly
supported.

EXAMPLES

Example 1

[0092]First, 11.8% by weight of silica-alumina fibers configured by 72% of
alumina and 28% of silica (average fiber length: 0.3 mm, average fiber
diameter: 5 μm), 5.9% by weight of glass fibers (average fiber
diameter: 9 μm, average fiber length: 0.1 mm), 17.0% by weight of
methyl cellulose as organic binder, 4.6% by weight of acrylic resin, 7.8%
by weight of a lubricant (UNILUB, made by NOF Corporation), 3.7% by
weight of a glycerin and 49.2% by weight of water were mixed and
sufficiently stirred so as to prepare a mixture.

[0093]Next, the mixture was charged into a cylinder of a plunger-type
molding machine, and a piston was pressed and shoved into the die side so
that the mixture was extruded through the die, thereby a raw molded body
was manufactured. The raw molded body was then dried at 200° C.
for 3 hours by a microwave drying apparatus and a hot-air drying
apparatus to remove moisture in the molded body. Next, heating treatment
was carried out on the molded body in an electric furnace at 400°
C. for 3 hours so that organic matters contained in the molded body were
removed.

[0094]Further, a heating treatment was carried out on the molded body in a
firing furnace at 950° C. for 5 hours, and thereafter, acid
treatment was carried out by immersing the molded body into a 4 mol/L HCl
solution of 90° C. for 1 hour and further a heating treatment was
carried out at 1050° C. for 5 hours so that a honeycomb structure
primarily comprising inorganic fibers having a size of φ30
mm×48 mm was obtained. In this honeycomb structure, the porosity of
the cell walls was 93%, the average pore diameter of the cell walls was
45 μm, the cell density was 8.5 cells/cm2 (55 cpsi); and the
thickness of the cell walls was 1.27 mm.

[0095]Next, a metal plate made of Ni--Cr alloy was processed in a round
disk shape having a size of φ30 mm×1 mm, and holes were formed
therein by a laser processing so that two plates of lamination members
for an end portion, having different sealed portions with one another, of
the honeycomb structure were manufactured.

[0096]One of the lamination members for an end portion was installed in
the cylindrical casing (can-type), and the honeycomb structure was placed
thereon in such a manner that the positions of holes of the lamination
member for an end portion fit to the positions of cells of the honeycomb
structure. Further, the other lamination member for an end portion was
also installed thereon in such a manner that the positions of holes
thereof fit to the positions of the cells of the honeycomb structure, and
the lamination member for an end portion was welded to the casing,
thereby a honeycomb filter with a length of 50 mm was manufactured.

[0097]Next, an oxide catalyst was supported on the obtained honeycomb
structure (honeycomb filter).

[0098]First, cerium nitrate was dissolved in water to prepare a solution
of a precursor of CeO2. A gas in which the solution of the precursor
was dispersed was transported by a carrier gas so as to be flowed into
one of the ends of the honeycomb filter. Here, the speed of the carrier
gas was adjusted to a space velocity of 72000 (1/h). In this manner, a
catalyst supporting honeycomb in which CeO2 having an average
particle diameter of 0.1 μm are supported on the honeycomb structure
comprising inorganic fibers was obtained. Here, the amount of the
CeO2 was adjusted to 20 g per 1 L of the catalyst supporting
honeycomb. Measurement of the average particle diameter of the oxide
catalyst was performed by using SEM photographs.

Comparative Example 1

[0099]First, 54.6% by weight of silicon carbide in a form of coarse powder
having an average particle diameter of 22 μm, 23.4% by weight of
silicon carbide in a form of fine powder having an average particle
diameter of 0.5 μm, 4.3% by weight of methyl cellulose as organic
binder, 2.6% by weight of a lubricant (UNILUB, made by NOF Corporation),
1.2% by weight of glycerin, and 13.9% by weight of water were mixed and
kneaded to obtain a mixture. Thereafter, the mixture was extrusion-molded
so as to manufacture a raw molded body.

[0100]Next, the raw molded body was dried by using a microwave drying
apparatus and the like to form a dried body, followed by filling of a
plug material paste having the same composition as that of the raw molded
body into the predetermined cells.

[0101]Further, after again dried by a drying apparatus, the resulting
product was degreased at 400° C. and then fired at 2200° C.
under a normal-pressure argon atmosphere for 3 hours so as to manufacture
a honeycomb structure formed by a silicon carbide sintered body with a
porosity of cell walls of 42%, an average pore diameter of 11.0 μm, a
size of φ30 mm×50 mm, the number of cells of 46.5 pcs/cm2
(300 cpsi) and a thickness of the cell walls of 0.25 mm.

[0102]Next, an oxide catalyst was supported on the honeycomb structure in
the same manner as in Example 1, thereby a catalyst supporting honeycomb
was obtained. Here, the average particle diameter of CeO2 was 0.1
μm, and the support amount was 20 g/L.

Comparative Example 2

[0103]A honeycomb structure was manufactured in the same manner as Example
1. The honeycomb structure was immersed in a solution containing 10 g of
CeO2, 40 ml of water and a pH adjusting agent for 5 minutes, and a
firing treatment was carried out on the resulting honeycomb structure at
500° C. so that a honeycomb structure on which a catalyst is
supported, having CeO2 supported thereon was manufactured. Here, the
average particle diameter of the supported CeO2 was 2 μm, and the
support amount was 20 g/L. The thus obtained honeycomb structure on which
a catalyst is supported was installed in the casing together with the
lamination members for an end portion in the same manner as in Example 1,
thereby a catalyst supporting honeycomb was manufactured.

(Evaluation Method)

[0104]A 2 L common rail engine was driven at a rotational speed of 1500
rpm with a torque of 47 Nm, and exhaust gases thus generated were allowed
to flow into the catalyst supporting honeycomb that was placed in a
branched pipe. Here, it was arranged to make it possible to heat the site
where the catalyst supporting honeycomb was placed by a heating device.
The catalyst supporting honeycomb was heated up to 350° C. by the
heating device, and the flow rate of the exhaust gases was set to 2.9
cm/s for the catalyst supporting honeycomb according to Comparative
Example 1, and was set to 18 cm/s for the catalyst supporting honeycomb
according to Example 1 and Comparative Example 2 so that a differential
pressure between the front and the back of the respective catalyst
supporting honeycombs was measured. The results are as shown in FIG. 5.

[0105]On the other hand, the prescribed temperatures and the flow rate
were set as shown in FIG. 6, and the continuous regeneration performance
for soot was evaluated according to the following equation.

mcont_reg=(min-maccum-mout)/t

[0106]In the above equation, each abbreviation refers to the following:

[0108]The results are shown in FIG. 7 in Arrhenius plot (the logarithms of
the both sides of the oxidizing velocity formula of C (carbon) shown by
the formula below were obtained, and the oxidation rate (g/m2/min)
of C is described on the vertical axis and the reciprocals of
temperatures (K) are described on the horizontal axis).

[0110]As compared with the catalyst supporting honeycomb of Comparative
Example 1, the catalyst supporting honeycomb of Example 1, which mainly
includes inorganic fibers, has a high porosity, and therefore an increase
with time in pressure loss in relation to the amount of soot that had
been flowed in can more easily be maintained at a low level. This is
because, by allowing soot to flow into deep portions of the cell walls,
soot can more easily be contacted with the catalysts supported inside the
cell walls. As a result of this, the soot flowed into the catalyst
supporting honeycomb can more easily be burned continuously, and thus a
time period before forced regeneration can more easily prolonged.

[0111]In the catalyst supporting honeycomb of Example 1, an average
particle diameter of the catalyst is at least about 0.05 μm and at
most about 1.00 μm, which is smaller as compared with the catalyst
supporting honeycomb of Comparative Example 2. Therefore, the activity
points between soot and the catalyst are increased, and soot can more
easily be burned continuously. On the other hand, since the activity
points between soot and the catalyst are few in the catalyst supporting
honeycomb of Comparative Example 2, soot tends to easily accumulate and
tends to plug pores in the deep portions. As a result of this, pressure
loss is more likely to increase significantly.

Other Embodiments

[0112]In the above, the embodiment according to the present invention has
been described; however, the present invention should not be construed as
limited to the embodiment. The present invention can be applicable to
various embodiments as long as they are within the scope of the gist of
the invention.

[0113]In the first embodiment mentioned above, the honeycomb structure 10a
formed by a single member was exemplified. However, a honeycomb structure
may be configured by a plurality of plate-like lamination members which
are laminated in such a manner that the cells of each lamination member
are aligned with the cells of the other lamination members.